Operators use gas lift valves in side pocket mandrels to lift produced fluids in a well to the surface. Ideally, the gas lift valves allow gas from the tubing annulus to enter the tubing through the valve, but prevent flow from the tubing to the annulus. A typical gas lift completion 10 illustrated in FIG. 1 has a wellhead 12 atop a casing 14 that passes through a formation. Tubing 20 positioned in the casing 14 has a number of side pocket mandrels 30 and a production packer 22. To conduct a gas lift operation, operators install gas lift valves 40 by slickline into the side pocket mandrels 30. One suitable example of a gas lift valve is the McMurry-Macco® gas lift valve available from Weatherford—the Assignee of the present disclosure. (McMURRY-MACCO is a registered trademark of Weatherford/Lamb, Inc.)
With the valves 40 installed, compressed gas G from the wellhead 12 is injected into the annulus 16 between the production tubing 20 and the casing 14. In the side pocket mandrels 30, the gas lift valves 40 then act as one-way valves by allowing gas flow from the annulus 16 to the tubing string 20 and preventing gas flow from the tubing 20 to the annulus 16. Downhole, the production packer 22 forces produced fluid entering casing perforations 15 from the formation to travel up through the tubing 20. Additionally, the packer 22 keeps the gas flow in the annulus 16 from entering the tubing 20.
The injected gas G passes down the annulus 16 until it reaches the side pocket mandrels 30. Entering the mandrel's ports 35, the gas G must first pass through the gas lift valve 40 before it can pass into the tubing string 20. Once in the tubing 20, the gas G can then rise to the surface, lifting produced fluid in the tubing 20 in the process.
As noted above, the installed gas lift valves 40 regulate the flow of gas from the annulus 16 to the tubing 20. To prevent fluid in the tubing 20 from passing out the valve 40 to the annulus 16, the gas lift valve 40 can use a check valve that restricts backflow.
One type of side pocket mandrel 30 is shown in more detail in FIGS. 2A-2B. This mandrel 30 is similar to a Double-Valved external (DVX) gas-lift mandrel, such as disclosed in U.S. Pat. No. 7,228,909 incorporated herein by reference in its entirety. The mandrel 30 has a side pocket 32 in an offset bulge from the mandrel's main passage 31. This pocket 32 holds the gas lift valve 40 as shown in FIG. 2B. The pocket's upper end has a seating profile 33 for engaging a locking mechanism of the gas lift valve 40, while the pocket's other end has an opening 34 to the mandrel's main passage 31.
Lower ports 36 in the mandrel's pocket 32 communicate with the surrounding annulus (16) and allow for fluid communication during gas lift operations. As shown in FIGS. 2A-2B, these ports 36 communicate along side passages 37 on either side of the pocket 32. When these passages 37 reach a seating area 39 of the pocket 32, these passages 37 communicate with the pocket 32 via transverse ports 38. In this way, fluid entering the ports 36 can flow along the side passage 37 to the transverse ports 38 and into the seating area 39 of the pocket 32 where portion of the gas lift valve 40 positions. As shown in FIG. 2B, the gas lift valve 40 has packings 43 that straddle and packoff the exit of the ports 38 in the mandrel's seating area 39. This is where inlets 42 of the gas lift valve 40 position to receive the flow of gas.
In the current arrangement, the ports 36 on the mandrel 30 can receive external check valves 50 that dispose in the ports 36. The check valves 50 allow gas G flow from the annulus (16) into the mandrel's ports 36, but prevent fluid flow in the reverse direction to the annulus (16). In general, the check valve 50 has a tubular body having two or more tubular members 52, 54 threadably connected to one another and having an O-ring seal 53 therebetween.
The upper end of the valve 50 threads into the mandrel's port 36, while the lower end can have female threads for attaching other components thereto. Internally, a compression spring 58 or the like biases a check dart 55 in the valve's bore against a seat 56. To open the one-way valve 50, pressure from the annulus (16) moves the check dart 55 away from the seat 56 against the bias of the spring 58. If backflow occurs, the dart 55 can seal against the seat 56 to prevent fluid flow out the check valve 50.
During gas lift, for example, the injected gas G can flow through the check valves 50, continue through separate flow paths in the ports 36 and passage 37, and then flow from the transverse ports 38 toward the inlets 42 of the gas lift valve 40. In turn, the gas lift valve 40 allows the gas G to flow downward within the valve 40, through a check valve 45, and eventually flow out through outlets 44 and into the side pocket 32. From there, the gas G flows out through the slot 34 in the mandrel 30 and into the production tubing (20) connected to the mandrel's main passage 31.
Because the gas lift valve 40 and the separate check valves 50 both prevent fluid flow from the tubing 20 into the annulus 16, they can act as redundant backups to one another. Moreover, the check valves 50 allow the gas lift valve 40 to be removed from the mandrel 30 for repair or replacement, while still preventing flow from the tubing 20 to the annulus 16. This can improve gas lift operations by eliminating the time and cost required to unload production fluid from the annulus 16 as typically encountered when gas lift valves are removed and replaced in conventional mandrels.
Various types of check valves can be used with gas lift valves or with other downhole components. For example, FIGS. 3A-3C illustrates types of prior art check valves for use with gas lift valves and mandrels. In particular, FIGS. 3A and 3B respectively show a CV-1 check valve 60A and a CV-2 check valve 60B from Weatherford's McMurry-Macco®CV series of reverse-flow check valves. These check valves 60A-B can attach to the bottom of a gas lift valve, to ports of a side pocket mandrel, or other flow-control device.
As shown, the check valves 60A-B each have an upper housing 62 threadably coupled to a lower housing 64 with an O-ring seal 63 therebetween. Disposed in the bore of the valves 60A-B, a dart 66 is biased by a spring 68 toward a seat 70. As shown in FIGS. 3A-3B, the seat 70 has an elastomeric component 72 and a retainer 74.
Another example of a check valve 60C is shown in FIG. 3C. This check valve 60C is similar to the DVX check valve available from Weatherford. This particular check valve 60C is well suited for a Double-Valved External (DVX) gas-lift mandrel described previously with reference to FIGS. 2A-2B. As shown, this check valve 60C includes an upper body 62 coupled to a lower body 64 by a port housing 65 and O-rings 63. As before, the check dart 66 can move in the port housing 65 against the bias of a spring 68 relative to a seat 70. Here, the seat 70 has a check seal 72 typically composed of elastomer (i.e., elastic polymer), such as nitrile butadiene rubber, hydrogenated nitrile butadiene rubber, fluorocarbon rubber, tetra-fluoro-ethylene-propylene, and perfluoroelastomers.
During a gas lift operation, upstream pressure typically from the surrounding annulus acts against the check valve 60A-C and is higher than the downstream pressure from the tubing. The pressure differential depresses the spring-loaded dart 66 in the valve 60A-C, allowing injection gas to flow through the check valve 60A-C and into the production tubing. If the downstream pressure is greater than the upstream pressure, flow across the check dart 66 forces the dart 66 against the seat 17, which prevents backflow. In the seating process, an elastomeric seal is first established between the dart 66 and elastomeric component 72. As the differential pressure increases, a metal-to-metal seal is then formed for additional protection between the dart 66 and portion of the lower housing 64 forming part of the seat 70.
As seen in FIGS. 3A-3C, check valves 60A-C for gas lift valves use elastomeric resilient seals 72 to provide a secondary seal to the metal-to-metal seal between the check dart 66 and the seat 70. As expected, such a dual seal protects against backflow, prevents casing from damage, and avoids costly workover operations. Unfortunately, the elastomeric seal 72 can be prone to explosive decompression during use.
In explosive decompression, the seal 72 is exposed to gas laden fluid at high pressure, and the compressed gas enters the interstices of the seal's elastomer. As long as operating pressures remain high, the seal 72 remains intact. Whenever the pressure falls, however, the gas in the elastomer of the seal 72 expands and can cause the seal 72 to rupture.
Explosive decompression has been a recognized problem in valve seals, and two solutions have been developed for handling it. In a first solution, specific types of elastomers have been developed that are more resistant than others to explosive decompression. An example of such an elastomer is FKM XploR V9T20, which is available from Trelleborg Sealing Solutions. Although these types of elastomers may be useful, even seals with such elastomers can still have issues with explosive decompression in check valves used for gas lift operations.
Another solution developed in the art has been to use only metal-to-metal sealing with no resilient seal in check valves. An example of such a check valve with only metal-to-metal sealing is the 15K Severe Service MTM Check Valve available from Halliburton. Although exclusive metal sealing may solve problems related to explosive decompression, a check valve utilizing only a metal-to-metal seal can be less reliable in sealing, especially if there is any debris present in the injection fluid. Moreover, the exclusive metal-to-metal seal can be costly to manufacture and maintain.
The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.